Search code examples
javaproject-loom

TLAB in Virtual Thread - Project Loom

How currently TLAB is handling in Virtual Thread introduced by Project Loom in Java? Is TLAB available in virtual threads?

Solution

  • Virtual threads don't have a TLAB - they don't need it.

    From Going inside Java’s Project Loom and virtual threads:

    Obviously, at some point, virtual threads must be attached to an actual OS thread to execute. These OS threads upon which a virtual thread executes are called carrier threads .

    If a virtual thread is not attached to a carrier thread is not executing any instructions and therefore cannot allocate memory - it doesn't need a TLAB.

    If it is attached to a carrier thread it is executing instructions and therefore can allocate memory. For this memory allocations it can safely use the TLAB of the carrier thread.

    No contention here:

    • at any point in time a carrier thread is executing exactly one virtual thread
    • at any point in time a virtual thread is executed by at most one carrier thread